1. Field of the Invention
The present invention relates generally to non-destructive measurement of local resistivity of semiconductors and, more particularly, to non-destructive measurement of local resistivity of semi-insulating InP substrates.
2. Description of the Related Art
The technology for manufacturing high-speed electronic and optoelectronic devices from periodic table group III-V materials has reached the stage where cost reduction through mass production techniques is the immediate goal. To maximize the effectiveness of mass production methods, non-destructive, automated evaluations need to be implemented throughout the manufacturing process. This is especially true for those device structures grown on semi-insulating (SI) InP substrates. The performance of these device structures, especially for the case of microwave devices, depends critically on the resistivity of the SI InP substrate. Because the aggregate experience with the bulk growth and processing of InP substrates, especially Fe-doped boules for SI InP substrates, is less than with GaAs substrates, variation in resistivity occurs from boule-to-boule and within the same boule. To meet the demands of mass production, both measurement and control of resistivity is necessary.
Present techniques of testing resistivity of semiconductor substrates are generally destructive. That is, present techniques of testing resistivity of semiconductor substrates consume the material tested, rendering it unfit for further use. For this reason, the present practice is to sacrifice a very small portion of a large semiconductor substrate wafer in the hopes that the test portion shares the same characteristics of the remaining portions of the wafer, often a very bad and costly assumption. Thus, there exists a need for nondestructive measurement of local resistivity of semiconductor substrates.
U.S. Pat. No. 4,953,983 to Bottka et al., issued Sep. 4, 1990, discloses an apparatus and method for nondestructive measurement of local carrier concentration and bandgap in a semiconductor using photoreflectance. However, U.S. Pat. No. 4,953,983 does not address the need for nondestructive measurement of local resistivity of semiconductor substrates.